Imagesetters and platesetters are used to expose the substrates in many conventional offset printing systems. Imagesetters are typically used to expose the film that is then used to make the plates for the printing system. Platesetters are used to directly expose the plates.
For example, plates are typically large substrates that have been coated with photosensitive or thermally-sensitive material layers, referred to the emulsion. For large run applications, the substrates are fabricated from aluminum, although organic substrates, such as polyester or paper, are also available for smaller runs.
Computer-to-plate printing systems are used to render digitally stored print content onto these printing plates. Typically, a computer system is used to drive an imaging engine of the platesetter. In a common implementation, the plate is fixed to the outside or inside of a drum and then scanned with a modulated laser source in a raster fashion.
The imaging engine selectively exposes the emulsion that is coated on the plates. After this exposure, the emulsion is developed so that during the printing process, inks will selectively adhere to the plate""s surface to transfer the ink to print medium.
Automated systems exist for handling the substrates before and after exposure in the imaging engine. These management systems typically pick individual substrates from cassettes and then feed the substrates to the imaging engine. Thereafter, the substrates are unloaded and passed on for further processing.
The plate must be properly feed into the imaging engine. These are high-resolution devices. They can compensate for some angular and positional misalignment of the plate on the drum, but if the positional or angular misalignment is too large, it can impact the performance of these imaging engines.
The present invention is directed to a substrate registration system for a substrate exposure machine, such as a platesetter or imagesetter. Specifically, it moves the plate or substrate to a known or desired position, so that the plate or substrate can then be properly inserted into the imaging engine and typically installed around its drum. Such registration is critical to the proper handling of plates in these plate management systems.
In general, according to one aspect, the invention features a substrate registering system for a substrate exposure machine. In a typical example, the substrate exposure machine is a platesetter or imagesetter. The substrate registering system comprises a substrate transfer system for supporting and conveying substrates in the substrate exposure machine. At least one engaging member is provided for pushing the substrates on the substrate transfer system to a desired position.
In a current implementation, the substrate transfer system comprises a frame and a series of rollers for supporting the substrates. The rollers are driven to convey the substrates relative to the substrate transfer system in the fashion of a conveyor. Typically, the substrates are moved from a substrate store to the imaging engine.
The engaging members extend typically in a direction that is orthogonal to the plane of the substrate transfer system. The engaging members move in a direction that is perpendicular to a direction in which the substrates are conveyed by the substrate transfer system. In this way, they can push the substrates to the desired position on the substrate transfer system.
In a preferred embodiment, at least one right engaging member and at least one left engaging member are provided to contact opposed sides of the substrates. In this way, they can move the substrates to a desired position, typically in the center of the substrate transfer system. This also allows the substrates to be angularly aligned.
In general, according to another aspect, the invention also features a method for moving plates in a platesetter. This method comprises picking plates from a plate store. The plates are then conveyed to an imaging engine for exposure. Prior to loading the plates in the imaging engine, however, the plates are registered to a desired position.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.